Arrangement for the controllable supply of at least two groups of electric lamps

ABSTRACT

Apparatus for controlling the energization of at least two groups of lamps each of which is in series with a thyristor wherein the control signal for all thyristors is generated in a common control signal generator. An auxiliary control signal generator is provided for each lamp group to control the lamp energy in the event of a failure of the main control signal.

United States Patent Bolhuis Jan. 28, 1975 ARRANGEMENT FOR THE [56] References Cited CONTROLLABLE SUPPLY OF AT LEAST UNITED STATES PATENTS TWO GROUPS OF ELECTRIC LAMPS 3.421.005 l/l969 Baker 315/159 x 75 I l 1 3,555,351 l/l97l Sherwin et al..... 1 menu" 2235,2333 g r gghggz 'l 3.601.652 8/197] Burnett. Jr. 315/156 x [73] Assignec: U .S. Philips Corporation, New lrinmry Examiner-Nathan Kaufman York, NY. Armrncy, Agem, or FirmFrank R. Trifari; Bernard 221 Filed: Apr. 4, 1973 Franzbli [21] Appl, No.: 347,927 [57] ABSTRACT Apparatus for controlling the energization of at least I30] Foreign Application priority Data two groups of lamps each of which is in series with a A r 20 972 Netherlands 7205292 thyristor wherein the control signal for all thyristors is p generated in a common control signal generator. An U S Cl 315/154 315/210 auxiliary control signal generator is provided for each a 6 39/04 lamp group to control the lamp energy in the event of [58] Field 61 Search 330/159, 154, 156 a mum Ofthe mam'comml 14 Claims, 3 Drawing Figures AC SUPPLY 51 l I 53 P23 CONTROL s11; GEN

PAH-1min JAN28I975 SHEET 1 UF 3 CONTROL SIG GEN Fig.1

AC SUPPLY PATENTED JAN 2 I975 .'-1.863.l04 SHEET 20F 3 ARRANGEMENT FOR THE CONTROLLABLE SUPPLY OF AT LEAST TWO GROUPS OF ELECTRIC LAMPS The invention relates to an arrangement for the controllable supply of at least two groups of electric lamps in which the lamps of each group are arranged in series with a controlled semiconductor switching element added to said group and in which the combination of a lamp group and the controlled semiconductor switching element added thereto is incorporated in a branch connecting two input terminals of the arrangement, a first control signal generator common to all semiconductor switching elements being present and having a connection to a control electrode of each of the controlled semiconductor switching elements.

An arrangement of the kind mentioned above is described, for example, in U.K. Pat. Spec. No. 1,092,509. In an embodiment in this U.K. patent the number of lamps per group is only one. This number may, however, alternatively be more than one. A drawback of the known arrangement is that when a control signal across the connection to the common control signal generator is not received in a lamp group, the relevant controlled semiconductor switching element remains non-conducting so that the lamp (or lamps) arranged in series therewith remains (remain) extinguished. Particularly when such a system is used for lighting tunnels a very dangerous traffic situation may occur because one or more sections of the tunnel may then be in complete darkness.

It has been proposed to use an electromagnetic switch in such cases for each lamp group which switch shunts the semiconductor switching element in the case of an interference. A drawback of this proposed embodiment is that a large number of these switches is generally required in that case and that they must each be proportioned for a large'lamp current.

An object of the invention is to provide a simple arrangement in which a control signal is still applied to the controlled semiconductor switching element even when the signal fromthe common control signal generator drops out, so that'the lamp (lamps) arranged in series with this switching element is (are) not completely extinguished.

According to the invention an arrangement for the controllable supply of at least two groups of electric lamps in which the lamps of each group are arranged in series with a controlled semiconductor switching element and in which the combination of a lamp group and the controlled semiconductor switching element added thereto is incorporated in a branch connecting two input terminals of the arrangement, while a first control signal generator common to all semiconductor switching elements is present which has a connection to a control electrode of each of the controlled semiconductor switching elements is characterized in that neareach lamp group is present as well an auxiliary supply source for control purposes of said lamp group and also an auxiliary control signal generator. In cases where no control signal is received across the connectionto the common-control signal generator in a lamp group the relevant auxiliary supply source and the relevant auxiliary control signal generator generate an auxiliary control signal for the control electrode of the controlled semiconductor switching element such that the luminosity of the lamp assumes a fixed value which at a maximum is equal to that which is present in the continuously conducting condition of the semiconductor switching element and which at a minimum is equal to 10 percent of said maximum value.

An advantage of such an arrangement according to the invention is that when for some reason or other the control signal from the common control signal generator does not arrive at a lamp group this lamp group does not remain extinguished, but that a simple auxiliary control signal controlling the luminosity ofthe lamp to a fixed value is generated with the aid of the auxiliary control signal generator added to said lamp group. This auxiliary control signal is a fixed signal which brings the luminosity of the lamps to, for example. the undimmed value, which is the maximum value, or to a minimum value which is at least 10 percent of the undimmed state. A value lower than that of the percent state (which is the undimmed state) is sometimes desirable, for example, in the case of the situation in a tunnel by night.

One of the reasons that no control signal is received near a lamp group across the connection to the common control signal generator may be, for example, that a defect has occurred in this common control signal generator. Another possibility is that a defect has occurred in the connection between this common control signal generator and the lamp group. Whatever the defect may be, the drop-out of the control signal at the area of the lamp group causes the control in an arrangement according to the invention to be taken over by the auxiliary control signal generator which for this purpose is fed from the auxiliary supply source present near the lamp group.

An arrangement according to the invention has the advantage relative to a known arrangement using an electromagnetic switch shunting the semiconductor switching element that only a control signal is to be generated and that the maximum lamp current need not flow through any extra elements.

To separate the control signal circuit from the lamp current circuit the connection between the common control signal generator and a control electrode of the controlled semiconductor switching element may employ, for example, a transformer.

in a preferred embodiment according to the invention the connection between the common control signal generator and a control electrode of one of the controlled semiconductor switching elements incorporates a coupling element which is free from energytransferring properties, particularly an opto-electronic coupling element.

Such a coupling element is generally much smaller and cheaper than a transformer. In the case of an arrangement according to the invention the use of a coupling element which is free from energy-transferring properties is especially advantageous because an auxiliary supply source near a lamp group is necessary anyway for generating the auxiliary control signal in case of interference. This auxiliary supply source may then also be used when there is no interference.

The indication whether a control signal is received across the connection to the common control signal generator or whether no control signal is received can be realized in different ways, for example, by means of a relay which in the presence of a control signal is in its energized condition and which has dropped out in the absence of a control signal.

In a preferred embodiment according to the invention in which a separate measuring section is present near a lamp group for indicating that no control signal has been received across the connection to the common control signal generator, this measuring section consists of a series arrangement of a capacitor and a resistor, which series arrangement is connected to the auxiliary supply source only in the presence of a control signal and in which the capacitor is provided with a discharge circuit in such a manner that the charge condition of the capacitor is a measure of the presence or absence of the control signal.

Such an arrangement has the advantage that the auxiliary control signal circuit can be activated in a simple manner with reference to the voltage condition of the capacitor.

In a further preferred embodiment of an arrangement according to the invention in which the auxiliary supply source is a direct voltage source, one of the terminals of the capacitor is connected to the base of a transistor and the other terminal of the capacitor is connected to a main electrode of this transistor.

An advantage of this preferred embodiment is that the auxiliary control signal generator can be activated with the aid of the latter transistor. The auxiliary control signal generator may be formed in different manners, for example, being provided with Zener diodes.

In a further preferred embodiment according to the invention the auxiliary control signal generator includes two gating circuits in which an input of the first gating circuit is connected to a main electrode of the transistor and in which a first input of the second gating circuit is connected to an output of the first gating circuit and in which a second input of the second gating circuit is connected to a junction between the series arrangement of the capacitor and the resistor at one end and the coupling element, which is free from energytransferring properties, at the other end, both gating circuits having the property that an input signal of low voltage results in an output signal of high voltage and that the output voltage is low when the two inputs receive a high voltage.

An advantage of the latter preferred embodiment is that when a square-wave voltage is generated by the common control signal generator this square-wave voltage may be passed unchanged to the output of the second gating circuit if there is no interference, whereas a permanent control signal rendering the relevant controlled semiconductor switching element permanently conducting can be generated when the signal from this common control signal generator remains absent.

In a further preferred embodiment of the latter arrangement the output of the second gating circuit is connected through an amplifier to the control electrode of the controlled semiconductor switching element.

An advantage of this embodiment is that always a signal of acceptable intensity can arrive at the control electrode of the controlled semiconductor switching element.

An arrangement according to the invention may operate, for example, with a direct current supply of the lamps. The semiconductor switching element is then, for example, a transistor.

In a further preferred embodiment of an arrangement according to the invention intended for the alternating current supply of lamps in which per lamp group two thyristors are present. i.e., one for each current direction, while an auxiliary control signal generator is present for each thyristor.

An advantage of this preferred embodiment is that even when a defect occurs simultaneously in the common control circuit and in one of the auxiliary control signal generators there is still an auxiliary control for the other thyristor which then results in a lamp luminosity being approximately 50 percent of its undimmed condition.

The auxiliary supply source may be formed. for example, as a separate battery.

In a preferred embodiment according to the invention the auxiliary supply source is the same as the supply source from which the lamps are fed.

Consequently, there is no further separate supply required in this case.

In a further preferred embodiment in which a measuring section is present near a lamp group for indicating the fact that no control signal is received across the connection to the common control signal generator a branch comprising a primary winding of a transformer is connected to the auxiliary voltage source in the absence of said control signal, and two secondary windings of this transformer are connected to control electrodes of two anti-parallel arranged controlled semiconductor rectifiers. In this case the auxiliary control generator is of a very simple type.

The latter preferred embodiment may be improved to such an extent that also the connection between the common control signal generator and the control electrodes includes a second primary winding of the transformer.

An advantage of this embodiment is that the transformer can be used both in the non-interfered and in the interfered condition.

An arrangement according to the invention is suitable whenever a controllable supply of lamps is used and whenever it is dangerous or undesirable that the lighting is completely extinguished in the case of a defect. An arrangement according to the invention is particularly suitable to be used for lighting a tunnel because especially in tunnels the drop-out of one or more lighting sections may lead to a dangerous situation for traffic.

The invention will be further described with reference to the accompanying drawing in which:

FIG. 1 shows an electrical circuit diagram of part of an arrangement according to the invention;

FIG. 2 shows two gating circuits which are diagrammatically shown in FIG. I; and

FIG. 3 shows part ofa second arrangement according to the invention.

In FIG. 1, input terminals l and 2 are intended to be connected to a supply voltage of, for example. 220 V, 50 Hz. 3 and 4 are low-pressure mercury vapour discharge lamps of, for example. 40 Watts. These lamps are provided with pre-heatable electrodes which are connected to heater-transformers 5 and 6. The lamp 3 is connected in series with an inductive ballast 7. Similarly the lamp 4 is connected to an inductive ballast 8. The other ends of the'ballasts 7 and 8 are connected to two anti-parallel arranged thyristors 9 and 10, respectively. The other ends of these thyristors are connected to the input terminal 2. A common control signal generator 20 is connected through two conductors 21 and 22 to an opto-electronic coupling element 23. This coupling element includes a light-emitting diode 53 as well as a photosensitive transistor 24. The coupling element 23 is present in the connection between the common control signal generator and the control electrode of the thyristor 10. This connection (including lines 50 and 51) serves to control the thyristor l0. ln the generator 20 a square-wave signal is generated whose phase is controllable relative to the voltage across the input terminals 1, 2. For controlling the thyristor 9 a subsequent coupling element 25, which is formed in the same manner as coupling element 23, is used in the control circuit of the thyristor 9. The coupling element 25 forms part of a circuit (not shown) which, via lines 50' and 51' ultimately applies a control voltage between the terminals 26 and 27 of the thyristor 9. The circuit section (not shown) between the coupling element 25 and the thyristor 9 and coupled to lines 50 and 51 is formed in a completely identical manner to the circuit section which is shown between the coupling element 23 and the thyristor 10. 28 denotes two further connections which lead to coupling elements similar to 23 and 25. These control a subsequent group of lamps (not shown). The connection 28 may lead to one pair of coupling elements or to two or three, etc., pairs of coupling elements. The circuits connected to the connections 28 are sometimes referred to as slave-dimmers. When the distance between the common control signal generator 20 and the coupling elements, for example, 23 and 25 is only short, this circuit is sometimes referred to a master dimmer.

The circuit which includes the transistor 24 will now be described in greater detail. An auxiliary direct voltage source 30 has a positive terminal connected to a capacitor 31 and to a resistor 32. The other end of this resistor 32 is connected to the collector of the transistor 24. The emitter of this transistor is connected to the negative terminal of the auxiliary direct voltage source 30. The resistor 32 is shunted by a series arrangement of the capacitor 31, a further resistor 33 and a diode 34. The junction between the capacitor 31 and theresistor 33 is connected through a resistor 35 to the base of a transistor 36. The positive terminal of the battery 30 is connected through a resistor 37 to the emitter of transistor 36. The collector of transistor 36 is connected to the negative terminal of the battery. The junction between the resistor 37 and the emitter of transistor 36 is connected to an input G1 of a first gating circuit whose output is denoted by Q1. A further input G2 of this gating circuit is not connected. Details of this gating circuit are found in FIG. 2. This gating circuit is fed through the terminals PQ which are also connected to the auxiliary direct voltage source 30. The output terminal Q1 of the first gating circuit is connected to the input terminal G3 of a second gating circuit. A second input G4 of this gating circuit is connected to the junction between the resistor 32 and the transistor 24. The output Q2 of this second gating circuit is connected through an amplifier 38 to the control electrode and to the cathode of the thyristor 10.

The operation of this circuit is as follows. A squarewave voltage is generated in the common control signal generator 20. This voltage is passed to the coupling elements 23 and 25, and to other (not shown) pairs of coupling elements of slave-dimmers which are connected to the connection 28. When the voltage of this block is in the direction which is the same as the pass direction of the diode of the coupling element 23, the diode becomes light-emitting and thereby renders the transistor 24 conducting. As a result the capacitor 31 is charged through the circuit 30, 31, 33, 34, 24, 30. During the next half cycle of the square-wave voltage of signal generator 20 the transistor 24 is nonconducting. The capacitor will then be discharged slightly via the circuit 31, 37, 36, 35. The time constant of this discharge circuit is, however, long (by proper choice of resistor 37) so that the discharge is relatively small. In this normal situation the capacitor 31 will therefore always maintain a given voltage so that the transistor 36 is in its conducting condition. This means that the input signal between G1 and the negative terminal of the battery 30 has a low voltage, that is to say, the voltage between Q1 and the negative terminal of battery 30 has a high value. This in itself means again that the input voltage at G3 of the second gating circuit has a high value which means that the output voltage Q2 of the second gating circuit is dictated by the input voltage at the input G4 of this second gating circuit. When transistor 24 is in the conducting condition, the voltage at G4 is low and hence at O2 is high, and conversely when the transistor 24 is in its non-conducting condition the voltage will be high at G4 and will be low at Q2. Thismeans that the signal which is passed from the second gating circuit to the amplifier 38 has exactly the same square-wave voltage, also as regards its phase, as that which is passed through the conductors 2], 22. Consequently this is the quite normal, interferencefree, situation. However, when an interference occurs either in generator 20 or in the conductors 21, 22 with the result that the coupling element 23 is no longer activated, transistor 24 remains permanently cut off. The capacitor 31 is then discharged so that also the transistor 36 is cut off and the input terminal G1 of the first gating circuit will then exhibit a high potential. The result is that the output terminal Q1 assumes a low voltage and this likewise applies to the input terminal G3 of the second gating circuit. This means that a highvalue signal is permanently available across the output Q2 which thereby permanently triggers the control electrode of thyristor 10 so that the luminosity of the lamps 3 and 4 is broughtinto the undimmed situation. In the case of a defect, the lamps 3 and 4 will thus not be extinguished but will be controlled to their lOO percent luminosity. Thus, this is effected with the aid of an auxiliary control signal generator comprising the transistor 36 and the two gating circuits. Similarly, as stated for the thyristor 10, the same is effected for the control of the thyristor 9 and also for other slave-dimmers" connected to the conductors 28 by means of similar auxiliary control signal generator means and amplifier means 38 (not shown).

The left-hand section in FIG. 2 shows the first gating circuit which is a gating circuit known per se. The righthand section shows the second gating circuit. The reference numerals indicating the inputs and outputs in FIG. 2 correspond to those in FIG. 1. Terminal P is connected to the positive terminal of the auxiliary direct voltage source 30 (see FIG. 1) and terminal Q is connected to the negative terminal of this battery.

In FIG. 2 the input terminal G1 is connected to a diode 100. The input terminal G2 is connected to a diode 101. The sides of the diodes and 101 remote from the input terminals G are connected together. The

junction between the diodes 100 and 101 is connected through a third diode 102 to a resistor 103. The other end of the resistor 103 is connected through a further resistor 104 to the positive supply terminal P, and through a series arrangement of a Zener diode 105 and two resistors 106 and 107 to the negative supply terminal Q. The terminals P and Q are also connected together through a series arrangement of a resistor 108, a transistor 109, a diode 110 and a further transistor 111. The output terminal Q1 of this first gating circuit is connected to the junction between the transistor 109 and the diode 110. This terminal O1 is connected to the input terminal G3 of the second gating circuit (see also FIG. 1).

The junction between the resistors 104 and 108 is furthermore connected to a resistor 112 the other end of which is connected to the base of the transistor 109. This base is furthermore connected to the junction between the diode 110 and the transistor 111.

Finally the junction of the transistor 109 and the diode 110 is also connected to a subsequent transistor 113. The other main electrode of the transistor 113 is connected to the base of the transistor 111. The base of the transistor 113 is in turn connected to the junction between the Zener diode 105 and the resistor 106.

The other section of FIG. 2 is built up in substantially the same manner as the section already described. The section described is the so-called first gating circuit (of FIG. 1) and the other section (right-hand section) of FIG. 2 is the second gating circuit.

The operation of the gating circuit is actually based on the fact that for a small potential difference between G1 and Q the transistor 109 is conducting and the transistor 111 is non-conducting so that the potential difference between 0, and Q is relatively high. For a large voltage difference between G1 and Q the two transistors 109 and 111 assume the opposite conducting conditions so that the voltage between Q1 and Q becomes relatively low.

FIG. 3 shows a further arrangement according to the invention. In this Figure input terminals 60 and 61 are intended to be connected to an alternating voltage of approximately 220 Volts, 50 Hz. 62 and 63 are two incandescent lamps. Box 64 is a common control signal generator which is comparable to generator of FIG. 1. Two conductors 65 and 66 of this generator 64 lead to a first primary winding 67 of a transformer, the other primary winding 68 of which can be switched on the terminals 60 and 61. The transformer has two secondary windings 69 and 70. Winding 69 is connected through a diode 71 to the control electrode of a thyristor 72. Winding 70 is connected through a diode 73 to a second thyristor 74, i.e., to the control electrode of this second thyristor. The thyristors 72 and 74 are arranged anti-parallel. Leads likewise pass from the cathode sides of the thyristors to the other sides of the said secondary windings of the transformer. The two thyristors are arranged in series with the incandescent lamps 62 and 63 between the input terminals 60 and 61, A threshold element (diac 75 and a first set of contacts 76a of a relay 76 are provided in series with the primary winding 68 of the transformer. 77 denotes a measuring section. The measuring section includes an opto-electronic coupling element 78 provided with a photosensitive transistor 79. The transistor 79 is arranged in series with an energizing coil of relay 76, which series arrangement is connected to the terminals ofa direct voltage source 80. Furthermore the said energizing coil is shunted by a capacitor 81.

In the interference-free condition the transistor 79 of the coupling element will be rendered periodically conducting by a signal originating from the control generator 64. As a result a current flows through the circuit 80, 79, 76, 80 which maintains the contact 76a open. In that case the capacitor 81 also is charged. This capacitor 81 is discharged in the non-conducting half cycles of the transistor 79 across the winding 76. As a result the relay remains permanently opened in the interference-free condition. In this interference-free case voltages will be induced in the normal manner through 64, 65, 66, 67 in the windings 69 and of the transformer, which voltages are passed to the control elec trodes of the thyristors 72, 74. However. when the control signal from signal generator 64 does not arrive. the transistor 79 of the coupling element 78 will no longer receive light so that no current flows in the circuit of the direct voltage source 80. As a result the relay winding 76 will no longer be energized and the relay contact 76a will close. The transformer winding 68 will then receive current through the input terminals 60 and 61. In that case this alternating voltage will be transferred via the winding 68 to the windings 69 and 70. Also in the case of FIG. 3 a section of lamps 62. 63 is thus provided with its own auxiliary control arrangement for generating an auxiliary control signal for the thyristors 72 and 74 in the event of the control generator 64 dropping out. Other slave-dimmers (not shown) each having a group of lamps are connected to the connections 82 of the control generator 64.

The breakdown voltage of the diac also determines the level of luminosity assumed by the lamps 62 and 63 after the occurrence of the interference in the control generator 64. In order to reduce this luminosity level to a relatively low level, for example, to ID percent of the undimmed luminosity, the relay 76 may be provided with another two pairs of contacts 761: and 760 as shown in FIG. 3. In fact, it can be achieved thereby that after the occurrence of an interference in the control generator 64 an extra resistor 83 is arranged in series with the incandescent lamps 62 and 63. If the contact 76a closes, the contact 76b opens and the contact 76c closes. It is of course alternatively feasible that in a further embodiment the auxiliary control signal generator is equipped with a fixed RC circuit so as to realize a given phase shift between the auxiliary control signal and the voltage across the input terminals (such as 60, 61) and thus to realize a given lamp luminosity in the case of interference.

What is claimed is:

1. Apparatus for controlling the illumination of at least two groups of electric lamps comprising, means connecting the lamps of each group in series with a controlled semiconductor switching element. two input terminals for coupling a source of electric energy to said lamps, means connecting the combination of a lamp group and its series controlled semiconductor switching element in a branch across the two input terminals of the apparatus, a first control signal generator common to all of the semiconductor switching elements and having a connection to a control electrode of each of the controlled semiconductor switching elements, each lamp group including an auxiliary electric energy supply source for controlling said lamp group and an auxiliary control signal generator. said auxiliary control signal generator being responsive to the absence of a control signal across the connection to the common control signal generator so that the relevant auxiliary supply source and the relevant auxiliary control signal generator generate an auxiliary control signal for the control electrode of its respective controlled semiconductor switching element such that the lamp luminosity assumes a fixed value which at a maximum is equal to that which occurs in the continuously conducting condition of the semiconductor switching element and which at a minimum is equal to percent of said maximum value.

2. An apparatus as claimed in claim 1 wherein the connection between the common control signal generator and a control electrode of one of the controlled semiconductor switching elements includes an optoelectronic coupling element.

3. An apparatus as claimed in claim 1 further comprising a separate measuring section present near a lamp group for indicating the presence or absence of a control signal across the connection to the common control signal generator, said measuring section comprising a series arrangement of a capacitor and a resistor with means connecting said series arrangement to the auxiliary supply source only in the presence of a control signal, a discharge circuit for the capacitor connected in circuit such that the charge condition of the capacitor is a measure of the presence of absence of the control signal.

4. An apparatus as claimed in claim 3 in which the auxiliary supply source is a direct voltage source and the discharge circuit includes means connecting one of the terminals of the capacitor to the base of a transistor and the other terminal of the capacitor to a main electrode of said transistor.

5. An apparatus as claimed in claim 4, wherein the auxiliary control signal generator includes two gating circuits in which an input of the first gating circuit is connected to a main electrode of the transistor and a first input of the second gating circuit is connected to an output of the first gating circuit and a second input of the second gating circuit is connected to a point in the measuring section which indicates the presence or absence of said control signal, both gating circuits having the property that an input signal of low voltage results in an output signal of high voltage and that the output voltage is low when the two inputs receive a high voltage.

6. An apparatus as claimed in claim 5 wherein the output of the second gating circuit is connected to the control electrode of the controlled semiconductor switching element.

7. An apparatus as claimed in claim 3, wherein the input terminals are adapted for connection to an alternating current supply and in which each lamp group includes two thyristors connected in anti-parallel, each for one current direction, and an auxiliary control signal generator is present for each thyristor.

8. An apparatus as claimed in claim 1 wherein the energy source coupled to the input terminals also serves as the auxiliary supply source.

9. An apparatus as claimed in claim 8 further comprising a measuring section present near a lamp group for indicating the presence or absence of-a control signal across the connection to the common control signal generator, characterized in that in the absence of the control signal a branch comprising a primary winding of a transformer is connected to the auxiliary supply source and that two secondary windings of said transformer are connected to control electrodes of two antiparallel arranged controlled semiconductor rectifiers.

10. An apparatus as claimed in claim 9 wherein the connection between the common control signal generator and the control electrodes includes a second primary winding of the transformer,

11. An electric supply apparatus for a plurality of electric lamps comprising, a pair of input terminals for coupling a source of electric energy to the lamps, a plurality of controlled semiconductor switching elements, means connecting a first switching element in series with at least one lamp in a first branch across said input terminals, means connecting a second switching element in series with at least one other lamp in a second branch across said input terminals, a control signal generator common to all of the switching elements. means connecting the output signal of said signal generator to the control electrodes of said switching elements to control the supply of electric energy to the lamps, a plurality of auxiliary control generators each individually coupled to a control electrode of a respective switching element for generating an auxiliary control signal therefor in the absence of the output control signal of the common signal generator at a particular switching element control electrode, and means responsive to the absence of the primary output control signal at one of more switching element control electrodes for activating the relevant auxiliary control generators to supply said auxiliary control signals to its as sociated switching elements so that the associated lamps are energized to emit a fixed value of luminance energy.

12. Apparatus as claimed in claim 11 wherein said activating means includes means for limiting the electric energy supplied to a lamp under auxiliary control to a fixed value which is a fraction of the energy supplied while the lamp is under the control of the common control signal generator.

13. Apparatus as claimed in claim 11 wherein said output signal connecting means comprises optoelectronic coupling means.

14. Apparatus as claimed in claim 13 wherein said auxiliary control generators include an RC circuit coupled to a DC voltage source and including a capacitor whose charge level is determined by the condition of the opto-electronic coupling means.

" IN THE SPECIFICATION mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 3 104 A Dated January 93 107';

I PIETER JAN BOLHUIS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2 line 66, cancel "has dropped" and insert drops-;

Col. 3, line 66, cancel "In a" and insert -A;

Col. 3, line 67, cancel "intended for the" and insert for use with an-;

Col. 4

, line 1, cancel "supply of lamps in which per lamp group" and insert lamp supply, includes;

Col. 4, line 2, cancel "are present" and insert per lamp Col. 4, line 41, change is group-;

to be-,-

Col. 4, lines 64-65, cancel respectively";

Col. 5, line 30, change "only" to fairly;

Col. 6, line 51, after "same" insert control;

cancel the control";

Col. 6, line 52, cancel "of" PAGE TWO UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,863,104 Dated January 28, 1975 lnventox-(s) PIETER JAN BOLHUIS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 7, line 21, after "to" insert the collector of-; G1

IN THE CLAIMS Claim 3 line ll, cancel. "of" eco d occurrence,

and insert -or- Signed and Scaled this sixteenth D ay Of September 19 75 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting ()fl'icer Commissioner nf'Parenls and Trademarks 

1. Apparatus for controlling the illumination of at least two groups of electric lamps comprising, means connecting the lamps of each group in series with a controlled semiconductor switching element, two input terminals for coupling a source of electric energy to said lamps, means connecting the combination of a lamp group and its series controlled semiconductor switching element in a branch across the two input terminals of the apparatus, a first control signal generator common to all of the semiconductor switching elements and having a connection to a control electrode of each of the controlled semiconductor switching elements, each lamp group including an auxiliary electric energy supply source for controlling said lamp group and an auxiliary control signal generator, said auxiliary control signal generator being responsive to the absence of a control signal across the connection to the common control signal generator so that the relevant auxiliary supply source and the relevant auxiliary control signal generator generate an auxiliary control signal for the control electrode of its respective controlled semiconductor switching element such that the lamp luminosity assumes a fixed value which at a maximum is equal to that which occurs in the continuously conducting condition of the semiconductor switching element and which at a minimum is equal to 10 percent of said maximum value.
 2. An apparatus as claimed in claim 1 wherein the connection between the common control signal generator and a control electrode of one of the controlled semiconductor switching elements includes an opto-electronic coupling element.
 3. An apparatus as claimed in claim 1 further comprising a separate measuring section present near a lamp group for indicating the presence or absence of a control signal across the connection to the common control signal generator, said measuring section comprising a series arrangement of a capacitor and a resistor with means connecting said series arrangement to the auxiliary supply source only in the presence of a control signal, a discharge circuit for the capacitor connected in circuit such that the charge condition of the capacitor is a measure of the presence of absence of the control signal.
 4. An apparatus as claimed in claim 3 in which the auxiliary supply source is a direct voltage source and the discharge circuit includes means connecting one of the terminals of the capacitor to the base of a transistor and the other terminal of the capacitor to a main electrode of said transistor.
 5. An apparatus as claimed in claim 4, wherein the auxiliary control signal generator includes two gating circuits in which an input of the first gating circuit is connected to a main electrode of the transistor and a first input of the second gating circuit is connected to an output of the first gating circuit and a second input of the second gating circuit is connected to a point in the measuring section which indicates the presence or absence of said control signal, both gating circuits having the property that an input signal of low voltage results in an output signal of high voltage and that the output voltage is low when the two inputs receive a high voltage.
 6. An apparatus as claimed in claim 5 wherein the output of the second gating circuit is connected to the control electrode of the controlled semiconductor switching element.
 7. An apparatus as claimed in claim 3, wherein the input terminals are adapted for connection to an alternating current supply and in which each lamp group includes two thyristors connected in anti-parallel, each for one current direction, and an auxiliary control signal generator is present for each thyristor.
 8. An apparatus as claimed in claim 1 wherein the energy source coupled to the input terminals also serves as the auxiliary supply source.
 9. An apparatus as claimed in claim 8 further comprising a measuring section presEnt near a lamp group for indicating the presence or absence of a control signal across the connection to the common control signal generator, characterized in that in the absence of the control signal a branch comprising a primary winding of a transformer is connected to the auxiliary supply source and that two secondary windings of said transformer are connected to control electrodes of two anti-parallel arranged controlled semiconductor rectifiers.
 10. An apparatus as claimed in claim 9 wherein the connection between the common control signal generator and the control electrodes includes a second primary winding of the transformer.
 11. An electric supply apparatus for a plurality of electric lamps comprising, a pair of input terminals for coupling a source of electric energy to the lamps, a plurality of controlled semiconductor switching elements, means connecting a first switching element in series with at least one lamp in a first branch across said input terminals, means connecting a second switching element in series with at least one other lamp in a second branch across said input terminals, a control signal generator common to all of the switching elements, means connecting the output signal of said signal generator to the control electrodes of said switching elements to control the supply of electric energy to the lamps, a plurality of auxiliary control generators each individually coupled to a control electrode of a respective switching element for generating an auxiliary control signal therefor in the absence of the output control signal of the common signal generator at a particular switching element control electrode, and means responsive to the absence of the primary output control signal at one of more switching element control electrodes for activating the relevant auxiliary control generators to supply said auxiliary control signals to its associated switching elements so that the associated lamps are energized to emit a fixed value of luminance energy.
 12. Apparatus as claimed in claim 11 wherein said activating means includes means for limiting the electric energy supplied to a lamp under auxiliary control to a fixed value which is a fraction of the energy supplied while the lamp is under the control of the common control signal generator.
 13. Apparatus as claimed in claim 11 wherein said output signal connecting means comprises opto-electronic coupling means.
 14. Apparatus as claimed in claim 13 wherein said auxiliary control generators include an RC circuit coupled to a DC voltage source and including a capacitor whose charge level is determined by the condition of the opto-electronic coupling means. 